The present invention relates to a device for indicating inadmissible length deviations of a perforated web, preferably a formaliner-perforated paper web to be used for the production of forms, where the printing press comprises at least one working mechanism provided with rotating working elements, such as at least one punching work for punching the perforations of the web, and possibly at least one printing unit, and where at least one transmitter receives values of the velocity of rotation of the working elements of the working mechanism and converts said values into pulses, and at least one transmitter receives values of the velocity of the web and converts said values into pulses and at least one measuring unit receives pulse information from the transmitters.
Upon treating a paper web in a printing press for the production of forms, for instance, the intended result requires a constant so-called "web-length". This is controlled mechanically by a so-called "in-feed variator" which is adapted to brake and thereby to stretch the paper web into a desired length and stretch during the feeding of the unprinted roll through the machine and on the finished roll.
At the same time as the paper is printed in the machine, one or two rows of control perforations are normally punched out (along one or both edges, respectively of the web). These perforations are called "formaliner-perforations" or "-holes" and are standard in practically all form production. These control perforations are used for conveying the paper web in subsequent-treatment machines, for instance (when a plurality of webs are superimposed as an invoice set or the like) or for instance in a customer's writer or data printer. It is very important, therefore, that such control perforations have a standardized spacing, 1/2 inch (tolerance at a web length of 3 m about .+-.0.5 mm), while otherwise misalignments may occur due to track-jumping of the web or non-alignment between the different webs.
As mentioned hereabove, the web stretching operation described will influence the length of the paper web, and thus also the mutual spacing of said form aligner holes. If the web is stretched forcefully, the web length will be reduced, thus also reducing the spacing between the form aligner holes so that this spacing becomes too short. If the web is slacked, the web length will increase, and the form-aligner hole-spacing will become too large.
Different paper qualities require different variator settings; the same paper may also vary from one roll to another. The web length is measured manually on a measuring table, and is then samples in the course of the production. Thus there is a demand of being able to measure and adjust the web length continuously in operation in order to prevent the web length from varying from one roll to the next, for example.
Such a measuring equipment, as mentioned hereinbefore, must be able to evaluate deviations less than .+-.0.5 mm at a measured web length of 3 m, which means maximum a tolerance of about .+-.1/6 of 0.5 mm (ca 1/6 of 3 m equals 1 cylinder cycle of the working tool and its pulse transmitter in the machine. This would require a transmitter with an enormous resolution (ca 10,000 pulses per cycle) for the intended sensibility or response, and this is a disadvantage since a printing press often generates vibrations which would be propagated to the transmitters and act on the latter, causing faulty indications as a result.